The invention relates to the art of electroplating certain specific areas of a continuous web of material. One example of such a material would be the lead frames upon which semiconductor chips are mounted for support and electrical connections. These lead frames are formed from a continuous web of metal which is plated in several different locations with precious metals by a plating machine such as described in U.S. Pat. No. 3,723,283. At each plating station, the web is clamped between masks that have apertures therein positioned to admit plating electrolyte only to desired areas. The masks typically cover enough of the web to simultaneously plate a number of discreet sets of chip pads. If for example, a spot is to be masked off on each set, a single support bar is used with a number of spaced projections, each of which has a small rubber like mask, in the shape of the spot to be protected, molded onto the surface of the projection. The bar is moved against the web so that each small rubber like mask contacts the correct portion of the web, and then plating is initiated.
In the prior art, the tiny spots to be protected must be positioned very accurately. Hence, a carefully machined metal bar is needed to define the exact locations. Each tiny mask is glued or molded directly to a projection on the bar so that it too will be in the exact right spot and of the exact shape and size. If just one of the fragile mask is damaged, the whole bar must be removed so that the damaged mask can be repaired. Considerable time is lost on the production line due to such repairs. My invention avoids this.